Clinical Features Associated with A. baumannii BSI Mortality Clinical Features Associated with Acinetobacter baumannii Bloodstream Infections Mortality in a Tertiary Hospital in Southern Brazil

Pedro Olimpio Siqueira Castilho^1*, Fernanda Martelli Takahashi¹, Maria Julia Onça Moreira¹, Larissa Sugiura¹, Alanis C Cardoso¹, Tatiana de Carvalho Caldas¹, Gabriela de Souza Barbosa¹, Marcia RE Perugini¹, Marsileni Pelisson¹, Floristher E Carrara¹, Eliana Carolina Vespero^1
1Laboratory of Clinical Microbiology, Department of Pathology, Clinical and Toxicological Analysis, Health Sciences Center, State University of Londrina, Brazil

*Correspondence author: Pedro Olimpio Siqueira Castilho, Laboratory of Clinical Microbiology, Department of Pathology, Clinical and Toxicological Analysis, Health Sciences Center, State University of Londrina, Brazil;
Email: [email protected]

Citation: Castilho POS, et al. Clinical Features Associated with A. baumannii BSI Mortality Clinical Features Associated with Acinetobacter baumannii Bloodstream Infections Mortality in a Tertiary Hospital in Southern Brazil. J Clin Immunol Microbiol. 2025;6(3):1-10.

Copyright^© 2025 by Castilho POS, et al. All rights reserved. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Table 1: Demographic and clinical data stratified by mortality from patients with A. baumannii BSI hospitalized between 2020 and 2023.

Discussion

The present study reports an increase in the number of A. baumannii clinical isolates, mainly CRAB, obtained over 10 years. Previous studies in Brazil reported that during COVID-19 pandemics, A. baumannii has become one of the main causes of secondary infections, being isolated mainly from tracheal aspirate (71.2%) and blood cultures (7.2%) particularly in ICUs, a similar profile as observed in the present study [4]. Overall, carbapenem resistance is highly prevalent in this species with resistance rates exceeding 70% in some regions, such as Eastern Europe, Africa and Asia [5]. In Brazil, carbapenem resistance rates reaches up to 80%. making infections caused by this pathogen difficult to treat, leading to worse prognoses and a higher risk of mortality [6].

In this scenario, A. baumannii is one of the leading causes of healthcare-acquired BSI. According to ASCENSION surveillance study, CRAB is responsible for 9.6% of all BSI in Brazil [7]. We observed an increasing A. baumannii BSI incidence rate from 2020 onwards, especially due to the COVID-19 pandemics. However, the impact of COVID-19 on BSI varies across studies. While some studies demonstrate that there was no increase in the incidence of BSI during the pandemic period, others, such as the present study, highlight an increase or a trend towards a higher incidence of BSI after 2020 [8-11].

A previous study carried out in the same institution as this one reported that between 2006 and 2016, 92.2% of BSI A. baumannii isolates were resistant to meropenem, thus we observed a small increase in the rate of resistance to meropenem, that now reaches 94.2%. Moreover, we also observed an increase in the rate of resistance to amikacin (41.7% to 91.2%) and gentamicin (69.9% to 84.1%). On the other hand, the resistance rates to ciprofloxacin and polymyxin B have decreased from 100.0% to 94.6% and 10.7% to 8.9%, respectively [12]. A similar study also observed increasing rates of resistance to carbapenems (64% to 98%) and aminoglycosides (11% to 85%) between 2019 and 2022, possibly associated with prior colonization by resistant strains, extensive use of invasive devices and antimicrobials and prolonged hospitalization, highlighting a trend of increasing resistance rates in clinical isolates of A. baumannii worldwide [13]. According to a systematic review, global resistance rate to polymyxins is 13%, thus polymyxins remain one of the most effective antimicrobials against MDR A. baumannii [14]. However, due to the high consumption of polymyxin to treat CRAB infections in the last few years, several studies in different countries have reported increasing polymyxin resistance rates A. baumannii.  Rocca and colleagues demonstrated a 10% increase in the colistin resistance rate in A. baumannii between 2016 and 2021 [15]. Another study also demonstrated a 37% increase in the colistin resistance rate between 2015 and 2022, reaching 42.5% in the last year. This increase poses a major global health problem, as the spread of strains resistant to these antimicrobials further limits therapeutic choices, leading to worse prognoses and higher mortality [16].

As expected, higher mortality rates were observed in infections caused by carbapenem and aminoglycoside resistant A. baumannii, mainly because these infections are often related to treatment failure. A cohort study demonstrated that MDR A. baumannii infections are associated with greater risk of mortality, risk of reinfections within 30 days and longer length of hospital stay, likely due to inappropriate initial antibiotic therapy, delay to active treatment and consequent increased severity of infection [17].

Similarly, several other clinical factors were also associated with mortality. Male patients presented higher chances of not surviving, which is consistent with findings from other studies that explain this association by the need for admission to intensive care units, higher risk of infection by MDR pathogens and polymicrobial infections [18]. Diabetes and systemic arterial hypertension are underlying conditions that were associated with higher mortality, several studies have reported the association between these comorbidities and A. baumannii bacteremia mortality, moreover other conditions such as chronic liver and kidney diseases, smoking and immunodeficiency are also commonly associated with higher mortality in this type of infection [19-21]. The use of several invasive devices, such as Indwelling Urinary Catheters (IUC), Central Venous Catheters (CVC), Mechanical Ventilation (MV), orotracheal nutrition tubes and hemodialysis, has also been associated with higher mortality. In general, prolonged use of these devices is a risk factor for A. baumannii infections in hospitalized patients, a meta-analysis study showed that patients using CVC and MV were approximately 3 times more likely to develop A. baumannii BSI, due to the potential for biofilm formation and direct access to the bloodstream or respiratory tract [22].

In this study, septic shock was strongly associated with mortality. Other studies have also determined sepsis as an independent risk and predictor of mortality in patients with A. baumanni BSI, increasing the risk of mortality by approximately 3-fold.  Therefore, early and effective empirical therapy is essential to reduce the likelihood of BSI progressing to septic shock [23,24]. Prior use of antimicrobials was also associated with the mortality of A. baumannii BSI. In our study, the use of 3^rd and 4^th generation cephalosporins, such as ceftriaxone and cefepime, was associated with higher mortality, but other studies mainly associate the previous use of carbapenems with higher risk in these infections, this happens because the prior use of these antimicrobials selects increasingly resistant strains that make treatment difficult, leading to therapeutic failure, worse prognoses and an increased risk of mortality [17,18]. Inappropriate empiric therapy significantly increases mortality rates in patients with CRAB infections. Studies have shown that patients who receive inadequate initial treatment have a mortality rate of up to 86% compared with 33.7% for those who receive appropriate therapy [25]. In this scenario, the main treatment for CRAB infections is the use of polymyxins or combination therapy using fluoroquinolones, aminoglycosides, ampicillin-sulbactam and carbapenems, in some cases, tigecycline is also an effective therapeutic option [17].

Overall, we observed a high mortality rate among patients with A. baumannii BSI, which is expected in these infections. Consistent with our findings, other studies also reported that patients with COVID-19 and A. baumannii coinfection had higher risk of mortality. These findings emphasize the negative impact of COVID-19 on patients with A. baumannii infection, highlighting risk factors common to both infections, such as prolonged ICU stays, use of multiple invasive devices and prior use of antimicrobials as empirical treatment [9,26].

Although our analysis included a wide range of potential risk factors, one limitation of the study is that this study represents a retrospective and single center analysis and may not apply to populations in other regions. Therefore, comparing our results with those from similar studies could help strengthen the development of a reliable model for predicting and reducing mortality risk factors in A. baumannii BSI.

Conclusion

This study demonstrates a significant increase in Acinetobacter baumannii Bloodstream Infections (BSI), particularly those caused by Carbapenem-Resistant Strains (CRAB), over the past decade. The rise in antimicrobial resistance especially to carbapenems, aminoglycosides and polymyxins has made treatment increasingly difficult, contributing to high mortality rates. The COVID-19 pandemic further exacerbated the incidence and severity of these infections, especially in ICU settings. Several clinical factors were associated with higher mortality, including male sex, underlying conditions like diabetes and hypertension, use of invasive devices, septic shock and prior antibiotic use. While this is a single-center, retrospective study, our findings are consistent with other reports and highlight the urgent need for improved infection control measures, early diagnosis and appropriate empirical therapy. Broader studies are needed to support the development of more effective strategies to reduce mortality from A. baumannii BSI.

Conflict of Interest

The authors declare that there is no conflict of interest.

Funding/Support

None.

Acknowledgements

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior is gratefully acknowledged for the funding. We also thank the Clinical and Laboratory Pathophysiology (State University of Londrina) for diagnostic support.

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